I came across a reference to OpenDNS too and have entered their addresses in this computer (which just happens to be a Mac). I'm not sure that using their DNS Server addresses is an better than those of my ISP.
If you want to try, open the Network Connections folder, right click your internet connection (modem connection) and select Properties. Highlight the entry for "Internet Protocol (TCP/IP)" and click the Properties button. In the next box, select "Use the following DNS Server addresses" and enter: